The role of reduced glutathione in preserving renal function and structure will be investigated, using the isolated perfused rat kidney as a model. We have preliminary evidence that glutathione depletion may produce lesions localized to the thick ascending limb associated with disproportionate reduction in concentrating ability. Specific inhibition of GSH synthesis and cellular depletion of GSH in a variety of ways will be employed, and an attempt made to correlate histological evidence of structural damage to cells and functional alterations, with tissue levels of reduced thiols, using both histochemical and enzymatic methods to evaluate this. The way in which Na-K-ATPase is activated when transepithelial transport is increased will be studied in the isolated perfused elasmobranch rectal gland. Intracellular sodium will be monitored non-invasively and sequentially by a new technique using nuclear magnetic resonance (23Na NMR). Steady-state levels of phosphorus intermediates will also be estimated with 31P NMR, together with the unidirectional rates of phosphate turnover, using the method of saturation transfer. Changes in intracellular electrical potential will be evaluated in separated tubules and cells before and after stimulation of transport, using fluorescent and radioactive probes. Alterations in ouabain binding of rectal gland cells will be assessed before and after secretion is stimulated. The possibility of interchange of pump enzyme between cell interior and plasma membranes by the mechanisms of exocytosis and of membrane internalization will be investigated. The possible role of protein kinase in activating cell membrane Na-K-ATPase will also be explored in direct experiments using partially purified enzyme and protein kinase prepared from rectal gland tissue.